Japanese Unexamined Patent Publication No. 2008-127706 discloses a sheet that prevents the return of liquids, which makes it difficult for a liquid to return to the skin side once it has been absorbed, dryness that does not allow liquid to be retained on the skin, wearability that does not cause a sense of discomfort when worn, and opacity that conceals the color of an absorbed liquid so as not to appear on the surface. This sheet is a corrugated sheet in which a plurality of grooves and ridges, respectively extending in one direction, are formed in a non-woven fabric, and the grooves and ridges are alternately arranged and mutually in parallel. The bottom portions of the grooves are flat over the direction in which they extend, and a plurality of openings are formed at prescribed intervals in the bottom portions. The ridges are formed convexly protruding from the back surface side towards the front surface side thereof in the form of projections, and the back sides of the non-woven fabric are in mutual contact at least at the bases of the protruding sites.
Japanese Unexamined Patent Publication No. 2007-167212 discloses a three-dimensional porous sheet capable of controlling the direction of diffusion of a liquid from ridges and facilitating bending of the ridges in the lengthwise direction. A plurality of ridges are formed in this sheet, openings are formed between mutually adjacent ridges, and sites that are relatively high and sites that are relatively low are alternately formed in the ridges in the lengthwise direction of the ridges.